All Questions

0
votes
1answer
44 views

Integral version of Ampere's law: who doesn't current outside the surface contribute to $\oint B\cdot d\ell$?

I have a question about why this is true $\oint B\cdot d\ell = \mu_0$ $I_{enclosed}$ My problem is that im not really seeing visually or mathematically why the magnetic field generated by a current ...
0
votes
1answer
23 views

Is it possible to have discontinuities in the phase portrait of a dynamical system? If yes what does it really mean?

I've been using Mathematica to draw the phase portrait of a system and I got some jumps along the trajectory. I have a deviation term which might be the reason of this but is it possible to have them ...
0
votes
2answers
29 views

Where does dispersion actually take place?

Out of 1 & 2, which is most accurate? And, out of 3 & 4, which is most accurate? Do they both agree with each other? Please explain?
0
votes
0answers
19 views

Flux through a cylinder located inside another perpendicular to it's axis [on hold]

A long cylindrical volume contains a uniformly distributed charge of density rho. Find the flux due to the elctric field through the curved surface of thr small cylinder whose axis is OP, and whose ...
0
votes
0answers
10 views

Wavelength vs change in angle of polarization?

My project is on polarimetry. I am searching for a base idea. What is the relationship between Wavelength vs change in angle of polarization? Note- Please do not lin this to optical activity(even ...
0
votes
0answers
17 views

Source for mathematical methods [duplicate]

I am just curious about any question and example sources for linear vector spaces, bra-ket notation, operators, commutators and hilbert spaces.
1
vote
2answers
36 views

Covariant surface vector

On pg 74 of Dalarsson's Tensors, Relativity and Cosmology (The Integral theorems for tensor field chapter), the covariant surface vector was defined as: $$dS_k=\frac{1}{2}\epsilon_{kmn}dx^mdx^n=\frac{...
0
votes
0answers
26 views

Well-definedness of Holstein-Primakoff transformation

In many-body physics, Holstein-Primakoff transformation is defined as follows: \begin{align} S_i^+ &= \sqrt{2S}(1-a_i^\dagger a_i/2S)^{1/2}a_i, \\ S_i^- &=\sqrt{2S}(1-a_i^\dagger a_i/2S)^{1/2}...
2
votes
2answers
51 views

Why is gaseous carbon dioxide transparent?

Some carbon-heavy products of combustion, e.g. soot, are black, as is carbon in other forms, e.g. graphite. This seems to suggest that carbon is black. But then how can $\text{CO}$ (carbon monoxide) ...
0
votes
0answers
13 views

Radius of wavelet using Huygen's principle

I was trying problem 1.6 and couldn't solve it. Any help is appreciated. My effort : I considered a point $P_1$ at distance y from the x-axis and another point $P_2$at a distance $y-\delta y$ from ...
2
votes
1answer
62 views

Relativistic quantum mechanics ${}$

I am reading Weinberg's book "Quantum theory of field". Сould you explain to me the following things? Vol.1, page 60: How are we equating the coefficients? How we find the formula (2.4.8)? 2.3.10: ...
1
vote
2answers
65 views

If a satellite speeds up, does that make move farther away or closer?

If a satellite is in a stable circular orbit and goes about 41% faster (escape velocity) then it leaves its host forever. I get that. However, what if it speeds up by less than 41%? Intuitively, it ...
12
votes
6answers
2k views

Can two people see the same photon?

In a dark room there are two people and a very faint candle. Then the candle emits one photon. Is it true that only one person can see the photon? Why? And are there any experiments?
0
votes
0answers
16 views

Electrons cannot sense electrostatic force?

Why there is not voltage or current just for 1ms if I connect a multimeter ground to the negative terminal of a DC power supply or charged capacitor? Why electrons in measure lead and DMM device ...
0
votes
0answers
12 views

Hydrostatic pressure

The solvent in which porous structure will create higher hydrostatic pressure at the beginning of the solvent removal process? I have two porous cakes, A and B with different height. A is 9.6 cm and B ...
3
votes
2answers
52 views

There are two velocities on the sphere. How to sum them on the sphere?

As shown in the figure, there are two velocities on the sphere, one is the velocity along the meridian direction, the arc length is its size, the other is the velocity along the equatorial direction, ...
0
votes
0answers
18 views

Branch of Physics that Examines Atoms Relationships

Is there a specific branch of physics that can examine and calculate the strengths of atomic or molecular bonds and predict how they are going to break, putting into consideration the surrounding ...
0
votes
0answers
12 views

A free electron is placed in the path of a plane electromagnetic wave. The electron will start moving [on hold]

Options 1. along the electric field 2. along the magnetic field 3. along the direction of propagation of the wave 4. in a plane containing the magnetic field and the direction of propagation ...
1
vote
1answer
55 views

Length contraction of an accelerating rod

Let us assume a rod of length, $4l$, initially at rest. The coordinates are defined s.t - (assuming uniform density) $$X_{back-end}(0) = -2l$$ $$X_{front-end}(0) = +2l$$ $$X_{mid-point}(0) = 0$$ ...
0
votes
0answers
10 views

What is the gravitational torque on a square frame?

A rigid wire is in the shape of a square of edge-lenth L, mass m and it carries a current I. The square lies on a flat horizontal surface, with a magnetic field of magnitude B is parallel to two edges ...
1
vote
0answers
21 views

Parabola black body heating

I'm having trouble figuring out why this following example of shenanigans wouldn't work. If you take a parabolic mirror (say from polished aluminium) with a magnification of M and construct it such ...
0
votes
1answer
19 views

Does moment of inertia only work for special cases?

I was looking into the moment of inertia expression for angular momentum. The angular momentum of a group of particles can be expressed as a linear transformation of the angular velocity vector. This ...
0
votes
1answer
29 views

Rotational Motion (angular momentum)

I don't understand why the angular momentum remains constant even after the distance of the particle (from the origin) keeps on increasing. Maybe I'm not reading the graph the way it is but I don't ...
-2
votes
0answers
33 views

Rain Car problem [on hold]

Rain falls with a speed of $10√2$ m/s. It makes 45° with vertical and 45° with a line drawn towards the north. Find the velocity with which car has to travel in the east direction so that for a person ...
-2
votes
0answers
21 views

Find the deceleration of a car during braking [on hold]

the question is: How do you find the deceleration of a car during braking, if you only know the stopping distance of 35.6m at 100km/h??
0
votes
0answers
18 views

How is the effective mass of electrons related to the specific heat of an electron gas? (in uniform magnetic field)

Just to make it clear, this is related to solid state physics. QUESTION How is the effective mass of electrons in uniform magnetic field related to the specific heat of an electron gas? DETAILS ...
0
votes
0answers
28 views

Density matrix expression by path integral

I came across an expression which I don't understand for the density matrix $\rho$ given by the path integral method (Fradkin, p.760) - $$ \left< \phi(x) \left| \rho\right| \phi\left(x'\right) \...
-1
votes
0answers
25 views

Hamiltonian is given of ising model in picture calculate the quantities [on hold]

How to solve this problem please help and help enter image description here
0
votes
2answers
37 views

Torque in a rubber band

So I have a bottle that moves with a propeller powered by a rubber band which when you twist the rubber band around and around, the bottle moves. I was wondering how torque plays in this. Is it that ...
3
votes
0answers
32 views

Dealing with thermodynamic processes in Statistical Mechanics

I have recently started studying Statistical Mechanics, and through my study of Classical Statistical Mechanics, I have studied how do we write distribution functions for equilibrium systems which can ...
0
votes
0answers
7 views

how is motion possible between a magnet and a superconductor

from my understanding of relative motion between a magnet and a conductor is that eddy currents work to oppose said motion but cannot entirely because of losses in the form of resistance, but without ...
0
votes
2answers
58 views

Question on using calculus in physics problem [on hold]

I did the following question: A smooth ring of mass $m$ can slide on a fixed horizontal rod. A string tied to the ring passes over a fixed pulley $B$ and carries a block $C$ of mass $M =2m$ as ...
2
votes
1answer
44 views

What is the information concept and how can it be measured,…?

According to the Wikipedia, ""Information of an entity is that which resolves the uncertainty of its properties"" source: Wikipedia, physical information Information contained in a physical ...
0
votes
1answer
27 views

Fusion Kinetic Energy

In fusion, the mass of the reactants is greater than the mass of the products. Thus, mass is lost in fusion. My thinking was that this mass defect is converted into binding energy that is then used to ...
0
votes
0answers
18 views

A point charge and a charged insulated conducting sphere

Suppose I have a insulated conducting sphere of radius a carries a change +Q. A point charge +q is placed at a distance d from the centre of the sphere. Find the minimum value of Q, which makes ...
0
votes
2answers
56 views

Why the gravity of a black hole is so strong by the Bad Astronomer

In this bad astronomer video, Phil Plait says two things: 1) He first demonstrates the effect of gravity using paper, and he keeps a fixed mass and distance. However as he makes the paper smaller and ...
1
vote
1answer
29 views

What is the point of including the gas constant in the dulong and petit law?

So why is the gas constant in $C=3R/M$? How does this relate to the specific heat capacity of a solid element?
1
vote
1answer
46 views

How do resistors form electric fields and thus potential drops?

$$V_{ab}=-\int_b^a\vec{E}*\vec{dl}=\int_a^b\vec{E}*\vec{dl}$$ By Kirchhoff's loop rule, the sum of the potential drops across a closed loop is zero. Going in the direction of conventional current ...
1
vote
2answers
55 views

What's meaning of velocity of electron?

How do we define velocity of microscopic particles at small scales. As for macroscopic particle we can scale the distance travelled by object. But this is not the case with electron. Still, while ...
-2
votes
0answers
64 views

Has this information relativity theory been disproven?

A talk was recently given by Ramzi Suleiman which covered an information relativity theory summarized in this PDF. This theory flies in the face of Einstein, Newton, and some other somewhat notable ...
0
votes
0answers
9 views

Equilibrium concentration of point defects in solids at sufficiently elevated temperature

Equilibrium concentration of point defects in solids is defined as $\chi=\exp(\frac{\Delta s}{k_B})\exp(\frac{-\Delta h}{k_BT})$. At high temperatures, may be even higher than melting temperature of ...
0
votes
1answer
24 views

Vacuum to hold object [on hold]

Can a 3-6V small motor create enough vacuum to lift and hold a porous object the size of an extra stength tylenol or peanut M&M? I am not an academic, but would appreciate any thoughts or advice.
1
vote
0answers
13 views

Stagnation pressure on an accelerating surface

The usual stagnation pressure $P_0$ on an object (e.g., a sphere) moving at velocity $U$ is simply $$ P_0 = P_\infty + \frac{\rho}{2}U^2$$ where $P_\infty$ is the pressure of the free stream. If ...
0
votes
1answer
19 views

Velocity of a rotating wheel with axle unlocked from wheel vs locked

For a bike wheel rolling down an incline as like the image, initially the axle of the wheel is not locked to the wheel, so the axle rotates as it moves down the incline but the wheel itself possesses ...
3
votes
1answer
100 views

Time evolution of a Gaussian wave packet, why convert to k-space?

I'm trying to do a homework problem where I'm time evolving a Gaussian wave packet with a Hamiltonian of $ \frac{p^{2}}{2m} $ So if I have a Gaussian wave packet given by: $$ \Psi(x) = Ae^{-\alpha x^...
1
vote
2answers
46 views

Tension in a rotating object

I'm somewhat stuck on this very simple question, but I can't convince myself of a satisfactory answer. I tried to look through the previous questions asked to avoid asking a duplicate I hope. Any ...
1
vote
3answers
67 views

Action of unitary operator on operator: two different definitions?

Defnition 1: Ref: Section 2.4.9, Quantum Mechanics: Concepts and Applications By Nouredine Zettili Ket $|\psi \rangle $ transform as $\underline{|\psi' \rangle = \hat{U} |\psi \rangle }$. Given ...
0
votes
1answer
46 views

Curl of Vectors

On pg. 71 of Dalarsson’s Tensors, Relativity and Cosmology 10.4 Curl of Vectors In an arbitrary $N$-dimenstional metric space the curl of a vector function $A_m$ is a second-order covariant ...
0
votes
1answer
55 views

Does an observer inside a black hole experience the de Sitter metric?

My question has emerged, because of the following similarities between the metric an observer experiences in the Schwartzschild space being under the Schwartzschild radius and an observer in the de ...
0
votes
0answers
29 views

Inner product axioms and Special Relativity

In Linear Algebra, an inner product is a function $(\cdot,\cdot): V \rightarrow F$ , where $V$ is a vector space over the field $F$. This function satisfies the usual three axioms (Conjugate symmetry, ...

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